In the field of mobile communication technologies, research and development of next generation communication systems are being conducted at a rapid pace. In a currently proposed next generation communication system, a single carrier scheme is to be used for uplink transmission to reduce the peak-to-average power ratio (PAPR) while achieving a wide coverage area. Also in this communication system, uplink and downlink radio resources are allocated to users according to their channel conditions in the form of shared channels to be shared by the users. The process of allocating radio resources is called “scheduling”. In order to perform uplink scheduling properly, each user device transmits a pilot channel to a base station and the base station estimates the uplink channel conditions of the user device based on the reception quality of the pilot channel. Similarly, in order to perform downlink scheduling properly, the base station transmits a pilot channel to the user device and the user device reports information indicating the reception quality of the pilot channel (i.e., channel quality indicator (CQI)) to the base station. Then, the base station estimates downlink channel conditions of the user device based on the reported CQI.
Meanwhile, an uplink control channel may include first control information (essential control information) that is always sent together with an uplink data channel or second control information that is sent regardless of the presence or absence of an uplink data channel. The first control information includes information that is necessary to demodulate a data channel such as a modulation scheme and a channel coding rate used for the data channel. The second control information includes a CQI, delivery confirmation information (ACK/NACK) for a downlink data channel, and/or a resource allocation request. A user device may transmit the first control information, the second control information, or both of them using uplink control channels.
In the proposed next generation communication system, when a resource block (radio resources) is allocated for transmission of an uplink data channel, the first control information and if necessary, the second control information are transmitted using the allocated resource block; and when no uplink data channel is to be transmitted, the second control information is transmitted using a dedicated resource block (dedicated frequency band). This method is described below in more detail.
FIG. 1 is a drawing illustrating an example of uplink frequency band allocation. In FIG. 1, two sizes of resource blocks (large resource blocks and small resource blocks) are provided. The large resource blocks have a bandwidth FRB1 of 1.25 MHz and a time period TRB of 0.5 ms. The small resource blocks have a bandwidth FRB2 of 375 kHz and a time period TRB of 0.5 ms. The time period may also be called a unit transmission period, a transmission time interval (TTI), or a subframe. One time period may correspond to the duration of one wireless packet. In FIG. 1, six resource blocks are arranged in the frequency direction and the small resource blocks are located at the right and left ends. Various arrangement patterns may be used to arrange resource blocks as long as they are known to the sending and receiving ends. In this exemplary uplink scheduling, control channels (first control channels) accompanying uplink data channels and second control channels (if necessary) are transmitted in parts of the time periods of the large resource blocks (the second, third, fourth, and fifth resource blocks). The small resource blocks (the first and sixth resource blocks) are allocated to control channels (second control channels) that are transmitted regardless of the presence or absence of uplink data channels. A second control channel of a user device may be transmitted using two small resource blocks. In this example, the second control channel of user device A is transmitted using the sixth resource block in the second subframe and the first resource block in the third subframe. Similarly, the second control channel of user device B is transmitted using the sixth resource block in the third subframe and the first resource block in the fourth subframe. In other words, a second control channel is transmitted using multiple frequency bands and time slots (i.e., the second control channel hops in the frequency and time directions). This method makes it possible to achieve frequency diversity gain and to increase the probability that the second control channel is properly demodulated by the base station.
FIG. 1 is drawn as if each small resource block is exclusively used by the corresponding user device. For example, resource blocks labeled “Control A” look like they are exclusively used by user device A. However, a resource block may be shared by multiple user devices. For example, the sixth resource block in the second subframe may be shared by user devices A and C. In this case, for example, user devices A and C share the resource block by frequency division multiplexing.
FIG. 2 is a drawing illustrating another example of uplink frequency band allocation. As in FIG. 1, two sizes of resource blocks are provided in FIG. 2. In this example, a time period TRB of each subframe of the small resource blocks (first and sixth resource blocks) is divided into two sub-periods. As shown in FIG. 2, a second control channel of user device A is transmitted using the sixth resource block in a first sub-period (the first half) of a third subframe and using the first resource block in a second sub-period (the second half) of the third subframe. Similarly, a second control channel of user device B is transmitted using the first resource block in the first sub-period of the third subframe and using the sixth resource block in the second sub-period of the third subframe. In other words, a second control channel is transmitted using multiple frequency bands and time slots (i.e., the second control channel hops in the frequency and time directions). This method makes it possible to achieve frequency diversity gain and to increase the probability that the second control channel is properly demodulated by the base station. Also, with this method, transmission of the control channel of user device A is completed within one subframe and transmission of the control channel of user device B is also completed within one subframe. Therefore, this method is preferable to reduce transmission delay of uplink control channels.
Also in FIG. 2, a resource block may be shared by two or more user devices. For example, the sixth resource block in the first sub-period of the third subframe may be shared by user devices A and B. In this case, user devices A and B may share the resource block by frequency division multiplexing as disclosed, for example, in 3GPP R1-061675.